I'd hardly call that even a moderate amount of carbon build up inside the chamber. The valve stems have a lot of gunk on them, but that happens to any direct injected engine without an effective way of removing oil vapour from the intake air. The turbo'd Minis have the same problem and BMW responds by blasting the intake valves with walnut shell to get rid of it. The excessive wear is scary, but I'm not totally surprised either; the ring can really tax an engine.